Method for Producing a Platinum Catalyst Precursor

ABSTRACT

The present invention relates to a method for producing a precursor of a supported platinum catalyst. To provide a method for producing a platinum catalyst precursor, by means of which supported platinum catalysts can be produced which have a relatively high activity, a method is proposed, comprising the steps of:
     a) impregnating an open-pored support material with platinum sulphite acid;   b) calcining the impregnated zeolite material under a protective gas.

The present invention relates to a method in particular for producing aprecursor of a supported platinum catalyst.

Supported noble metal catalysts, in which relatively small noble metalparticles are deposited on the surface of a solid support, are used inparticular in synthetic chemical and petrochemical processes in order toconvert a wide variety of educts into desired intermediate products orend products or to chemically refine different cuts of petroleumprocessing. In addition, supported noble metal catalysts are inparticular also used as oxidation catalysts in the purification ofexhaust gases from combustion engines.

Supported catalysts loaded with noble metal are normally produced bymeans of a multi-stage method. For example, in a first step a supportmaterial is impregnated with a noble metal salt solution of the desirednoble metal. After the removal of the solvent from the support materialin a subsequent step, the support material is then calcined in a furtherstep, wherein the noble metal can be converted to an oxide form bythermal treatment. Then, in a further step, the noble metal component isconverted to the catalytically active, highly dispersed noble metal ofoxidation state 0, for example by means of hydrogen, carbon monoxide orwet-chemical reducing agent. The supported noble metal catalyst can bestabilized for storage purposes in a final step, for example by wetstabilization by means of an oil or by dry stabilization by means ofpreoxidation (passivation) of the deposited noble metal particles.

The activity of supported noble metal catalysts normally depends on thesize of the noble metal particles. The supported noble metal catalystsknown in the state of the art have the disadvantage that they becomeless active in the course of their use because of a sintering of thenoble metal particles into larger units accompanied by a reduction incatalytically active surface. The speed of this so-called thermal ageingprocess depends on the temperature level at which the catalyst is used.To be precise, as the operating temperature increases so does the speedof said ageing process, which is assumed to be caused by an increasedmobility of the noble metal particles on the support material surfaceaccompanied by an increased tendency to sinter.

A large number of attempts have already been made in the state of theart to produce catalysts which have a high activity when used at hightemperatures and are subject to only a low thermal ageing process.Kubanek et al., “Microporous and Mesoporous Materials 77 (2005) 89-96”,for example describe the production of a supported platinum catalyst byimpregnating a zeolite of the structure type MFI (SH27) with the Ptprecursor compound Pt(NH₃)₄(NO₃)₂ and then calcining the zeolite loadedwith the precursor compound in a protective gas atmosphere. WhenPt(NH₃)₄(NO₃)₂ is used, autoreduction occurs at relatively hightemperatures. However, the thus-produced supported platinum catalyst hasa relatively low activity as well as a relatively high tendency tothermal ageing.

An object of the present invention is therefore to provide a method inparticular for producing a platinum catalyst precursor, by means ofwhich supported platinum catalysts can be produced which have anincreased activity compared with the platinum catalysts known from thestate of the art.

Furthermore, an object of the present invention is to provide a methodfor producing a platinum catalyst precursor, by means of which supportedplatinum catalysts can be produced which display a relatively lowtendency to thermal ageing and accordingly maintain their catalyticactivity almost unchanged over long service lives.

This object is achieved by a method comprising the steps of:

-   a) impregnating an open-pored support material with platinum    sulphite acid;-   b) calcining the impregnated support material under a protective    gas.

It was surprisingly discovered that, by means of the method according tothe invention, a platinum catalyst precursor can be obtained which,after the conversion of the platinum component to the oxidation state 0,results in a supported platinum catalyst which is characterized by anincreased activity.

In addition, it was surprisingly established that, by impregnating anopen-pored support material with platinum sulphite acid and calciningthe impregnated support material in a protective gas atmosphere, aplatinum catalyst precursor can be obtained by means of which, byreduction of the platinum component into the oxidation state 0, asupported platinum catalyst can be produced which displays a very lowtendency to thermal ageing at relatively high temperatures and maintainsits catalytic activity largely unchanged over relatively long servicelives.

These advantages of a platinum catalyst produced via the methodaccording to the invention are brought to bear in particular during useat high temperatures, such as for example in oxidation catalysis inwhich corresponding platinum catalysts produced in conventional ways areprone to a rapid thermal ageing because of a high mobility of theplatinum particles caused by the predominantly high temperaturesaccompanied by an increased tendency to sinter.

Platinum catalyst precursors and from these, following reduction,finally supported platinum catalysts can be produced by means of themethod according to the invention, i.e. supported platinum catalystswhich comprise Pt of oxidation state 0. The platinum catalysts can beboth metal catalysts which, in addition to Pt of oxidation state 0,contain one or more additional transition metals of any oxidation stateor of oxidation state 0, preferably noble metals, and pure platinumcatalysts which contain only Pt of oxidation state 0 as catalyticallyactive metal. If, in addition to Pt, a further transition metal ofoxidation state 0 is also present in the platinum catalyst, the metalscan be present in the form of particles of pure metal or in the form ofalloy particles. To produce platinum catalysts which, in addition to Pt,also comprise at least one further transition metal of oxidation state0, e.g. Ag, in the framework of the method according to the inventionthe open-pored support material can for example be impregnated withplatinum sulphite acid and with a further corresponding transition metalcompound before the metal components are converted to the oxidationstate 0.

It is pointed out that the catalysts obtainable via the method accordingto the invention are not limited to catalysts in which only Pt ispresent as metal. It is also conceivable that, in addition to platinum,metal oxides that are difficult to reduce are also present.

In one step of the method according to the invention, the open-poredsupport material is impregnated with platinum sulphite acid. Platinumsulphite acid is known in the state of the art and is often called “PSA”there. Platinum sulphite acid is assigned the Chemical Abstract Number61420-92-6 and is freely available on the market, for example fromHeraeus, Hanau, Germany as 10.4% platinum sulphite acid solution.

In the method according to the invention, the platinum sulphite acid ispreferably used in the form of an aqueous platinum sulphite acidsolution containing 0.01 to 15 wt.-% Pt (metal). It is further preferredto use the platinum sulphite acid in the form of an aqueous platinumsulphite acid solution containing 0.1 to 8 wt.-% Pt (metal) in themethod according to the invention, more preferably in the form of anaqueous platinum sulphite acid solution containing 1 to 6 wt.-% Pt(metal) and particularly preferably in the form of an aqueous platinumsulphite acid solution containing 2.5 to 3.5 wt.-% Pt (metal). It ismost preferred to use the platinum sulphite acid in the form of anaqueous platinum sulphite acid solution containing 2.8 to 3.3 wt.-% Pt(metal) in the method according to the invention.

According to a preferred embodiment of the method according to theinvention, the method furthermore comprises the step of: converting theplatinum component of the calcined platinum sulphite acid to theoxidation state 0. The support material impregnated with platinumsulphite acid is subjected to a reducing step after the calcining. Wherethe method according to the invention comprises the above-named step ofconverting the platinum component of the calcined platinum sulphite acidto the oxidation state 0, the method according to the invention relatesto a method for producing a supported platinum catalyst, wherein theplatinum catalyst can comprise, in addition to Pt of oxidation state 0,one or more further transition metals, in particular noble metals, ofoxidation state 0.

The platinum component of the calcined platinum sulphite acid can beconverted to the oxidation state 0 both by wet-chemical route, i.e. bymeans of a solution with a reducing effect, and by dry-chemical route,i.e. by means of a gas with a reducing effect. It is preferred accordingto the invention that the platinum component of the calcined platinumsulphite acid is converted to the oxidation state 0 by dry-chemicalroute. As a result there is the possibility of carrying out thereduction in a procedurally simple way at relatively high temperatures,which promotes a rapid and complete reduction of the platinum component.

According to a further preferred embodiment of the method according tothe invention, it is provided that the platinum component of thecalcined platinum sulphite acid is converted to the oxidation state 0 ata temperature of at least 100° C. In this connection, it is preferredthat the platinum component is reduced at a temperature of from 100° C.to 400° C., more preferably at a temperature of from 200° C. to 350° C.,further preferably at a temperature of from 275° C. to 325° C. andparticularly preferably at a temperature of 300° C.

As has already been stated above, it can be preferred according to theinvention that the platinum component of the calcined platinum sulphiteacid is converted to the oxidation state 0 by dry-chemical route. Inprinciple any gaseous or gasifiable reducing agent can be used, by meansof which the platinum component can be reduced, such as for examplehydrogen, carbon monoxide, ethylene or methanol, ethanol, etc. Accordingto a particularly preferred embodiment of the method according to theinvention, it is provided that the platinum component of the calcinedplatinum sulphite acid is converted to the oxidation state 0 by means ofhydrogen.

If hydrogen is used as reducing agent, it can be preferred that thehydrogen is diluted with an inert gas such as for example nitrogen or anoble gas such as helium, neon, argon, krypton and/or xenon, whereinnitrogen is particularly cost-efficient and is accordingly preferredaccording to the invention. For example, the conversion of the platinumcomponent of the calcined platinum sulphite acid to the oxidation state0 by reduction in an atmosphere consisting of 0.1 wt.-% to 100 wt.-%hydrogen, preferably 3 to 5 wt.-% hydrogen, and the remainder inert gasis preferred according to the invention.

For example, the conversion of the platinum component of the calcinedplatinum sulphite acid to the oxidation state 0 by reduction in anatmosphere consisting of 10 wt.-% to 60 wt.-% hydrogen, preferably 15 to30 wt.-% hydrogen, and the remainder inert gas is furthermore preferredaccording to the invention.

In order to largely minimize the sulphur content of the platinumcatalyst resulting from the method of the invention, it can be providedaccording to a further preferred embodiment of the method according tothe invention that the steps of calcining the impregnated supportmaterial under protective gas and of converting the platinum componentof the calcined platinum sulphite acid to the oxidation state 0 arecarried out several times. For example, the two named method steps caneach be carried out 2, 3, 4 or 5 times, wherein the platinum componentis converted to the oxidation state 0 after every single calcining step.

It is further preferred within the meaning of the present invention thatthe reduction is carried out for a duration of at least 1 minute,preferably at least 30 minutes, further preferably at least 1 hour andmost preferably of at least 3 hours, wherein a duration of 4 or 5 hoursis most preferred.

Within the framework of the present invention, the open-pored supportmaterial can be impregnated with platinum sulphite acid in principleaccording to any method known to a person skilled in the art from thestate of the art and considered to be suitable. Examples of methods thatare preferred according to the invention are spraying a platinumsulphite acid solution onto the support material, dipping the supportmaterial into a platinum sulphite acid solution or the so-calledincipient wetness method (pore-filling method), in which there is addedto the support material a volume of solution corresponding to the volumeof its pores.

If the platinum sulphite acid solution is to be applied by spraying thesolution onto the support material, the spraying-on can be carried outaccording to the present invention by any spraying method known to aperson skilled in the art from the state of the art.

If it is provided that the platinum sulphite acid solution is to beapplied by dipping the support material into the solution, this iscarried out by first dipping the support material into the platinumsulphite acid solution and then—for example by suction—removing from itsolution not adhering to the support material surface.

It is particularly preferred according to the invention that the supportmaterial is impregnated with platinum sulphite acid by means of theincipient wetness method. In this method, the open-pored supportmaterial is loaded with a solution of the impregnating agent—hereplatinum sulphite acid, wherein the volume of the solution correspondsto the pore volume of the support material, which is why, after beingloaded with the solution, the zeolite material is outwardly dry and withit pourable. The incipient wetness method is also known to a personskilled in the art by the name pore-filling method.

The open-pored support material of the present invention is any supportmaterial which is known to a person skilled in the art as suitable forthe purpose according to the invention. The open-pored support materialis preferably an inorganic open-pored support material.

It is further preferred that the open-pored support material is asupport material with monomodal or with multimodal pore distribution.

According to a further preferred embodiment of the method according tothe invention, the support material comprises a material selected fromthe group consisting of titanium oxide; γ-, θ- or Δ-aluminium oxide;cerium oxide; silicon oxide; zinc oxide; magnesium oxide;aluminium-silicon oxide; silicon carbide and magnesium silicate or amixture of two or more of the above-named materials. It can furthermorebe preferred that the support material consists of one of theabove-named materials or mixtures.

According to a further preferred embodiment of the method according tothe invention, it is provided that the support material is a zeolitematerial. By a zeolite material is meant within the framework of thepresent invention according to a definition of the InternationalMineralogical Association (D. S. Coombs et al., Can. Mineralogist, 35,1997, 1571) a crystalline substance with a structure characterized by aframework of tetrahedra linked together. Each tetrahedron consists offour oxygen atoms which surround a central atom, wherein the frameworkcontains open cavities in the form of channels and cages which arenormally occupied by water molecules and extra-framework cations whichcan often be exchanged. The channels of the material are large enough toallow access to guest compounds. In the hydrated materials, thedehydration mostly occurs at temperatures below about 400° C. and is forthe most part reversible.

According to a further preferred embodiment of the method according tothe invention, it is provided that the zeolite material is a microporousor a mesoporous zeolite material. By the terms “microporous zeolitematerial” and “mesoporous zeolite material” are to be understoodaccording to the classification of porous solids according to IUPAC(International Union of Pure and Applied Chemistry) zeolite materialsthe pores of which have a diameter of less than 2 nm and a diameter offrom 2 nm to 50 nm respectively.

The zeolite material to be used in the method according to the inventioncan preferably correspond to one of the following structure types: ABW,ACO, AEI, AEL, AEN, AET, AFG, AFI, AFN, AFO, AFR, AFS, AFT, AFX, AFY,AHT, ANA, APC, APD, AST, ASV, ATN, ATO, ATS, ATT, ATV, AWO, AWW, BCT,BEA, BEC, BIK, BOG, BPH, BRE, CAN, CAS, CDO, CFI, CGF, CGS, CHA, CHI,CLO, CON, CZP, DAC, DDR, DFO, DFT, DOH, DON, EAB, EDI, EMT, EON, EPI,ERI, ESV, ETR, EUO, EZT, FAR, FAU, FER, FRA, GIS, GIU, GME, GON, GOO,HEU, IFR, IHW, ISV, ITE, ITH, ITW, IWR, IWV, IWW, JBW, KFI, LAU, LEV,LIO, LIT, LOS, LOV, LTA, LTL, LTN, MAR, MAZ, MEI, MEL, MEP, MER, MFI,MFS, MON, MOR, MOZ, MSE, MSO, MTF, MTN, MTT, MTW, MWW, NAB, NAT, NES,NON, NPO, NSI, OBW, OFF, OSI, OSO, OWE, PAR, PAU, PHI, PON, RHO, RON,RRO, RSN, RTE, RTH, RUT, RWR, RWY, SAO, SAS, SAT, SAV, SBE, SBS, SBT,SFE, SFF, SFG, SFH, SFN, SFO, SGT, SIV, SOD, SOS, SSY, STF, STI, STT,SZR, TER, THO, TON, TSC, TUN, UEI, UFI, UOZ, USI, UTL, VET, VFI, VNI,VSV, WEI, WEN, YUG and ZON, wherein zeolite materials of the structuretype Beta (BEA) are particularly preferred. The above nomenclature ofthree-letter codes corresponds to the “IUPAC Commission of ZeoliteNomenclature”.

Also preferred according to the invention are the members of mesoporouszeolite materials of the family which are combined under the name “MCM”in the literature, wherein this name is not a particular structure type(cf. http://www.iza-structure.org/databases). Mesoporous silicates whichare called MCM-41 or MCM-48 are particularly preferred according to theinvention. MCM-48 has a 3D structure of mesopores, through which thecatalytically active metal in the pores is particularly easilyaccessible. MCM-41 is preferred in particular and has a hexagonalarrangement of mesopores with uniform size. The MCM-41 zeolite materialhas an SiO₂/Al₂O₃ molar ratio of preferably more than 100, morepreferably of more than 200 and most preferably of more than 300.Further preferred mesoporous zeolite materials which can be used withinthe framework of the present invention are those which are called MCM-1,MCM-2, MCM-3, MCM-4, MCM-5, MCM-9, MCM-10, MCM-14, MCM-22, MCM-35,MCM-37, MCM-49, MCM-58, MCM-61, MCM-65 or MCM-68 in the literature.

Which zeolite material is to be used in the method according to theinvention primarily depends on the purpose of use of the catalyst to beproduced by means of the method according to the invention. A largenumber of methods are known in the state of the art to tailor theproperties of zeolite materials, for example the structure type, thepore diameter, the channel diameter, the chemical composition, the ionexchangeability as well as activation properties, to a correspondingpurpose of use.

The zeolite material to be used in the method according to the inventioncan be for example a silicate, an aluminium silicate, an aluminiumphosphate, a silicon aluminium phosphate, a metal aluminium phosphate, ametal aluminium phosphosilicate, a gallium aluminium silicate, a galliumsilicate, a boroaluminium silicate, a boron silicate or a titaniumsilicate, wherein aluminium silicates and titanium silicates areparticularly preferred.

By the term “aluminium silicate” is meant according to the definition ofthe International Mineralogical Association (D. S. Coombs et al., Can.Mineralogist, 35, 1997, 1571) a crystalline substance with spatialnetwork structure of the general formulaM^(n+)[(AlO₂)_(x)(SiO₂)_(y)]xH₂O, which is composed of SiO_(4/2) andAlO_(4/2) tetrahedra which are linked by common oxygen atoms to form aregular three-dimensional network. The atomic ratio of Si/Al=y/x isalways greater than/equal to 1 according to the so-called “Löwenstein'srule” which prohibits two neighbouring negatively charged AlO_(4/2)tetrahedra from occurring next to each other. Although more exchangesites are available for metals at a low Si/Al atomic ratio, the zeoliteincreasingly becomes more thermally unstable.

Within the framework of the present invention, the above-named zeolitematerials can be used in the method both in the alkaline form, forexample in the Na and/or K form, and in the alkaline earth form,ammonium form or in the H form. In addition, it is also possible to usethe zeolite material in a mixed form.

According to a further preferred embodiment of the method according tothe invention, it can be provided that a drying step occurs between stepa) and step b).

The drying step is carried out between the impregnating and thecalcining. The drying temperature is preferably between 25° C. and 250°C., more preferably between 50° C. and 200° C., further preferablybetween 100° C. and 180° C. and particularly preferably 120° C.

Drying is preferably carried out over a period of more than 1 min, morepreferably over a period of more than 1 h, further preferably over aperiod of more than 5 h and still more preferably over a period of morethan 12 h, wherein a drying time of 10 h can be particularly preferred.In this connection, it can moreover be advantageous if the duration ofthe drying step does not exceed a period of 48 h, preferably does notexceed a period of 24 h.

By the term “calcining” is generally meant heating at high temperatureswith the aim of for example materially or structurally altering thetreated material or a component thereof. A thermal decomposition, aphase transition or the removal of volatile substances for example canbe achieved by a calcining.

Within the framework of the present invention, the calcining ispreferably carried out in a temperature range of from 300° C. to 1200°C., more preferably in a temperature range of from 300° C. to 1000° C.,further preferably in a temperature range of from 400° C. to 950° C.,particularly preferably in a temperature range of from 700 to 900° C.and most preferably in a temperature range of from 730° C. to 900° C.

It is moreover particularly preferred that the calcining is carried outat a temperature of at least 750° C. During a calcining at a temperatureof at least 750° C., supported platinum catalysts which, despite highplatinum loading of for example 3 wt.-% relative to the weight of theplatinum and the open-pored support material, are largely free ofsulphur can be obtained by means of the method according to theinvention. Thus, by means of the method according to the invention, forexample platinum catalysts can be produced which contain 1 to 5 wt.-%platinum, relative to the weight of the platinum and the supportmaterial, and have a sulphur content of less than 0.004 wt.-%, relativeto the weight of the platinum and the support material. A low sulphurcontent is particularly advantageous, as sulphur acts as a catalystpoison in particular with regard to noble metals.

The heating rate during the calcining is preferably 0.5° C./min to 5°C./min, more preferably 1° C./min to 4° C./min and particularlypreferably 2° C./min.

The duration of the calcining at maximum temperature is preferably in arange of from 1 min to 48 h, more preferably in a range of from 30 minto 12 h and particularly preferably in a range of from 1 h to 7 h,wherein a calcining duration of 5 h or 6 h is particularly preferred.

Within the framework of the present invention, the calcining is carriedout under a protective gas. By protective gas are meant gases or gasmixtures which can be used as inert protective atmosphere, for exampleto prevent unwanted chemical reactions. Within the framework of thepresent invention, in particular the noble gases helium, neon, argon,krypton or xenon can be used as protective gas, or mixtures of two ormore of the above-named, wherein argon is particularly preferred asprotective gas. Besides the noble gases or in addition to them, nitrogenfor example can also be used as protective gas.

A typical method provided by the present invention comprises the stepsof:

-   -   a) impregnating an open-pored support material, in particular a        zeolite material, in particular a zeolite material of the        structure type BEA or a zeolite material from the MCM family,        preferably an aluminium silicate or titanium silicate zeolite        material, with platinum sulphite acid, in particular with a        platinum sulphite acid solution, preferably according to the        incipient wetness method;    -   b) calcining, preferably at a temperature above 750° C., the        impregnated support material under protective gas, preferably        under argon;    -   c) optionally converting the platinum component of the calcined        platinum sulphite acid to the oxidation state 0, preferably by        reduction by means of hydrogen, preferably at a temperature of        at least 100° C.

The present invention furthermore relates to a catalyst precursor or acatalyst that can be obtained according to the method according to theinvention. By means of the method according to the invention, supportedplatinum catalysts can be obtained which are characterized by anincreased activity as well as by an increased resistance to thermalageing compared with the corresponding platinum catalysts known in thestate of the art, or catalyst precursors can be obtained which can beconverted into platinum catalysts with said advantages.

In particular the present invention relates to a catalyst precursor thatcan be obtained by a method comprising the steps of:

-   -   a) impregnating an open-pored support material, in particular a        zeolite material, preferably a zeolite material of the structure        type BEA or a zeolite material from the MCM family, with        platinum sulphite acid according to the incipient wetness        method;    -   b) drying the impregnated support material over a period of 12 h        at a temperature of 120° C.;    -   c) calcining the impregnated and dried support material over a        period of 5 h at 790° C. under argon.

In particular the present invention relates in addition to a supportedPt catalyst that can be obtained by a method comprising the steps of:

-   -   a) impregnating an open-pored support material, in particular a        zeolite material, preferably a zeolite material of the structure        type BEA or a zeolite material from the MCM family, with        platinum sulphite acid according to the incipient wetness        method;    -   b) drying the impregnated support material over a period of 12 h        at a temperature of 120° C.;    -   c) calcining the impregnated and dried support material over a        period of 5 h at 790° C. under argon;    -   d) converting the platinum component of the calcined platinum        sulphite acid to the oxidation state 0 by reducing the platinum        component by means of a gas consisting of 5 vol.-% hydrogen in        nitrogen over a period of 5 h at a temperature of 300° C.

The present invention furthermore relates to a catalyst comprising anopen-pored support material, which is preferably a zeolite material, aswell as platinum of oxidation state 0, wherein the XRD spectrum of thecatalyst is free of signals of elemental platinum. Such catalysts can beproduced by means of the method according to the invention. It ispresumed that the XRD spectrum of the catalyst is free of Pt signals, asthe outer surface of the support material is substantially free orcompletely free of metal particles of a size to be able to diffractX-radiation according to the diffraction pattern of platinum.

The zeolite material of the catalyst according to the invention can beunderstood to mean according to a definition of the InternationalMineralogical Association (D. S. Coombs et al., Can. Mineralogist, 35,1997, 1571) a crystalline substance with a structure characterized by aframework of tetrahedra linked together. Each tetrahedron consists offour oxygen atoms which surround a central atom, wherein the frameworkcontains open cavities in the form of channels and cages which arenormally occupied by water molecules and extra-framework cations whichcan often be exchanged. The channels of the material are large enough toallow access to guest compounds. In the hydrated materials, thedehydration mostly occurs at temperatures below about 400° C. and is forthe most part reversible.

According to a further preferred embodiment of the catalyst according tothe invention, it is provided that the zeolite material is a microporousor a mesoporous zeolite material. By the terms “microporous zeolitematerial” and “mesoporous zeolite material” are to be understoodaccording to the classification of porous solids according to IUPAC(International Union of Pure and Applied Chemistry) zeolite materialsthe pores of which have a diameter of less than 2 nm and a diameter offrom 2 nm to 50 nm respectively.

The zeolite material of the catalyst according to the invention canpreferably correspond to one of the following structure types: ABW, ACO,AEI, AEL, AEN, AET, AFG, AFI, AFN, AFO, AFR, AFS, AFT, AFX, AFY, AHT,ANA, APC, APD, AST, ASV, ATN, ATO, ATS, ATT, ATV, AWO, AWW, BCT, BEA,BEC, BIK, BOG, BPH, BRE, CAN, CAS, CDO, CFI, CGF, CGS, CHA, CHI, CLO,CON, CZP, DAC, DDR, DFO, DFT, DOH, DON, EAB, EDI, EMT, EON, EPI, ERI,ESV, ETR, EUO, EZT, FAR, FAU, FER, FRA, GIS, GIU, GME, GON, GOO, HEU,IFR, IHW, ISV, ITE, ITH, ITW, IWR, IWV, IWW, JBW, KFI, LAU, LEV, LIO,LIT, LOS, LOV, LTA, LTL, LTN, MAR, MAZ, MEI, MEL, MEP, MER, MFI, MFS,MON, MOR, MOZ, MSE, MSO, MTF, MTN, MTT, MTW, MWW, NAB, NAT, NES, NON,NPO, NSI, OBW, OFF, OSI, OSO, OWE, PAR, PAU, PHI, PON, RHO, RON, RRO,RSN, RTE, RTH, RUT, RWR, RWY, SAO, SAS, SAT, SAV, SBE, SBS, SBT, SFE,SFF, SFG, SFH, SFN, SFO, SGT, SIV, SOD, SOS, SSY, STF, STI, STT, SZR,TER, THO, TON, TSC, TUN, UEI, UFI, UOZ, USI, UTL, VET, VFI, VNI, VSV,WEI, WEN, YUG and ZON, wherein zeolite materials of the structure typeBeta (BEA) are particularly preferred. The above nomenclature ofthree-letter codes corresponds to the “IUPAC Commission of ZeoliteNomenclature”.

Also preferred according to the invention are the members of mesoporouszeolite materials of the family which are combined under the name “MCM”in the literature, wherein this name is not a particular structure type(cf. http://www.iza-structure.org/databases). Mesoporous silicates whichare called MCM-41 or MCM-48 are particularly preferred according to theinvention. MCM-48 has a 3D structure of mesopores, through which thecatalytically active metal in the pores is particularly easilyaccessible. MCM-41 is preferred in particular and has a hexagonalarrangement of mesopores with uniform size. The MCM-41 zeolite materialhas an SiO₂/Al₂O₃ molar ratio of preferably more than 100, morepreferably of more than 200 and most preferably of more than 300.Further preferred mesoporous zeolite materials which can be used withinthe framework of the present invention are those which are called MCM-1,MCM-2, MCM-3, MCM-4, MCM-5, MCM-9, MCM-10, MCM-14, MCM-22, MCM-35,MCM-37, MCM-49, MCM-58, MCM-61, MCM-65 or MCM-68 in the literature.

Which zeolite material is contained in the catalyst according to theinvention primarily depends on the purpose of use of the catalystaccording to the invention. A large number of methods are known in thestate of the art to tailor the properties of zeolite materials, forexample the structure type, the pore diameter, the channel diameter, thechemical composition, the ion exchangeability as well as activationproperties, to a corresponding purpose of use.

The zeolite material of the catalyst according to the invention can befor example a silicate, an aluminium silicate, an aluminium phosphate, asilicon aluminium phosphate, a metal aluminium phosphate, a metalaluminium phosphosilicate, a gallium aluminium silicate, a galliumsilicate, a boroaluminium silicate, a boron silicate or a titaniumsilicate, wherein aluminium silicates and titanium silicates areparticularly preferred.

By the term “aluminium silicate” is meant according to the definition ofthe International Mineralogical Association (D. S. Coombs et al., Can.Mineralogist, 35, 1997, 1571) a crystalline substance with spatialnetwork structure of the general formulaM^(n+)[(AlO₂)_(x)(SiO₂)_(y)]xH₂O, which is composed of SiO_(4/2) andAlO_(4/2) tetrahedra which are linked by common oxygen atoms to form aregular three-dimensional network. The atomic ratio of Si/Al=y/x isalways greater than/equal to 1 according to the so-called “Löwenstein'srule” which prohibits two neighbouring negatively charged AlO_(4/2)tetrahedra from occurring next to each other. Although more exchangesites are available for metals at a low Si/Al atomic ratio, the zeoliteincreasingly becomes more thermally unstable.

In the catalyst according to the invention, the above-named zeolitematerials can be present both in the alkaline form, for example in theNa and/or K form, and in the alkaline earth form, ammonium form or inthe H form. In addition, it is also possible that the zeolite materialis present in a mixed form, for example in an alkaline/alkaline earthmixed form.

According to a further preferred embodiment of the catalyst according tothe invention, it is provided that the catalyst comprises 1 to 10 wt.-%platinum, relative to the weight of the platinum and the supportmaterial. It was found that, by means of the method according to theinvention, supported platinum catalysts can be obtained the XRD spectraof which are free of platinum signals despite relatively high platinumloading and which have a high resistance to thermal ageing despiterelatively high platinum loading. Moreover, it can be provided in thisconnection according to a further preferred embodiment of the catalystaccording to the invention that the catalyst comprises 1 to 10 wt.-%platinum, relative to the weight of the platinum and the supportmaterial, more preferably 2 to 5 wt.-%, further preferably 2.2 to 4.5wt.-%, particularly preferably 2.5 to 3.5 wt.-% and most preferably 3wt.-%.

According to a further preferred embodiment of the catalyst according tothe invention, it is provided that the catalyst is free of furthermetals of oxidation state 0.

As already stated above, according to a preferred embodiment of thecatalyst according to the invention, the support material is a zeolitematerial of the structure type Beta or a zeolite material from the MCMfamily.

Furthermore, it can be provided according to a further preferredembodiment of the catalyst according to the invention that the BETsurface area of the zeolite material is 100 to 1500 m²/g, preferably 150to 1000 m²/g and more preferably 200 to 600 m²/g. The BET surface areais to be determined according to the single-point method by adsorptionof nitrogen according to DIN 66132.

According to a further preferred embodiment of the catalyst according tothe invention, it can be provided that the catalyst is formed as powder,as shaped body or as monolith. Preferred shaped bodies are for examplespheres, rings, cylinders, perforated cylinders, trilobes or cones and apreferred monolith is for example a honeycomb body.

By the dispersion of a supported metal catalyst is meant the ratio ofthe number of all surface metal atoms of all metal particles of asupport to the total number of all metal atoms of the metal particles.In general it is preferred if the dispersion value is relatively high,as in this case as many metal atoms as possible are freely accessiblefor a catalytic reaction. This means that, given a relatively highdispersion value of a supported metal catalyst, a specific catalyticactivity of same can be achieved with a relatively small quantity ofmetal used. According to a further preferred embodiment of the catalystaccording to the invention, the dispersion of the platinum particles is50 to 100%, preferably 55 to 90%, further preferably 60 to 90%,particularly preferably 75 to 85%. The values of the dispersion are tobe determined by means of hydrogen according to DIN 66136-2.

In principle, it is advantageous if the platinum is present in thecatalyst according to the invention in particles as small as possible,as the platinum particles then have a very high degree of dispersion.However, a favourable average particle diameter also depends on theapplication in which the catalyst is to be used, as well as on the poredistribution and in particular the pore radii and channel radii of thesupport material. According to a preferred embodiment of the catalystaccording to the invention, the metal particles have an average diameterwhich is smaller than the pore diameter and is larger than the channeldiameter of the support material. The metal particles are therebymechanically caught in the support material, which leads to a highresistance to thermal ageing of the catalyst according to the invention.For example, the metal particles have an average diameter of from 0.5 to5 nm, preferably an average diameter of from 0.5 to 4 nm, morepreferably an average diameter of from 0.5 to 3 nm and particularlypreferably an average diameter of from 0.5 to 2 nm. The average particlediameter is preferably to be determined by decomposition of the supportmaterial and measuring the remaining Pt particles by means oftransmission electron microscopy (TEM).

The present invention furthermore relates to the use of a catalystaccording to the invention in a catalysis process which is carried outabove a temperature of 700° C.

According to a preferred embodiment of the use according to theinvention, the catalysis process is a purification of industrial orautomotive exhaust gases, such as preferably car, ship, train exhaustgases, etc.

The following examples serve in connection with the drawing toillustrate the invention. There are shown in:

FIG. 1: XRD spectrum of a first catalyst (1) according to the inventionproduced according to the method according to the invention as well asof a first comparison catalyst (2);

FIG. 2: Propane conversion of the first catalyst (squares), of the firstcatalyst after ageing (circles) and of the first comparison catalyst(triangles) in the heating phase against the temperature;

FIG. 3: Propane conversion of the first catalyst (squares) and of thefirst comparison catalyst (triangles) in the constant temperature phase(550° C.) against time;

FIG. 4: Propane conversion of the first catalyst (squares) and of thefirst comparison catalyst (triangles) in the cooling phase against thetemperature;

FIG. 5: XRD spectra (in sections) of a second catalyst (11) according tothe invention produced according to the method according to theinvention as well as a second (13) and a third (12) comparison catalyst;

FIG. 6: Propane conversion of the second catalyst (11) according to theinvention, of the second comparison catalyst (13) and of the thirdcomparison catalyst (12) in the heating phase against the temperature.

EXAMPLE 1

A powdery aluminium silicate zeolite material (20 g) of the structuretype Beta (BEA) in the H form with an Si/Al2 atomic ratio of 35 wasimpregnated with 21.9 ml of an aqueous platinum sulphite acid solutioncontaining 3.2 wt.-% Pt (calculated as metal) by means of the incipientwetness method. The absorption of water of dried BEA is (over night at120° C.) 9.2 g H₂O/10 g BEA. 12.96 g H₂O was added to the PSA solution.The solution had a Pt concentration of 3.2 wt.-% (the impregnation wascarried out with this solution).

After the impregnation, the zeolite material was dried over night at atemperature of 120° C.

After the drying, the impregnated zeolite material was calcined in anargon atmosphere over a period of 5 h at a temperature of 770° C. Theheating rate was 2° C./min and the argon volumetric flow rate during theheating and calcining phase was 2 l/min.

After the calcining, the zeolite material loaded with platinum wasreduced at a temperature of 300° C. by means of a gas containing 5vol.-% hydrogen in nitrogen (2 l/min) over a period of 5 h. The heatingrate was 2° C./min.

EXAMPLE 2

The catalyst obtained according to Example 1 was calcined in order toage it for a period of 10 h at a temperature of 650° C. in air (heatingrate: 10° C./min).

COMPARISON EXAMPLE 1

A catalyst was produced analogously to Example 1, with the onlydifference that the calcining took place in air.

XRD Measurement 1:

The catalyst produced according to Example 1 and Comparison Example 1was measured by X-ray diffractometry. The measured XRD spectra arerepresented in FIG. 1, wherein the spectrum of Example 1 and ofComparison Example 1 are given the reference numbers 1 and 2respectively.

The XRD spectrum of the catalyst produced according to Example 1(calcining under argon) displays no Pt signals, whereas the XRD spectrumof the catalyst produced according to Comparison Example 1 (calcining inair) displays clear Pt signals. In fact the signal at a 2-theta value ofabout 40° is the Pt(110) reflection (110 are the Miller indices), thesignal at a 2-theta value of about 46.5° is the Pt(200) reflection.

The absence of Pt reflections in the catalyst according to Example 1 isan indication that, despite the relatively high calcining temperature,no larger platinum clusters have formed on the outer surface of thezeolite material and the platinum is present in the zeolite materialpredominantly in highly dispersed form.

Elemental Analysis:

Within the framework of a completed elemental analysis, it wasestablished that the catalyst according to Example 1 has a sulphurcontent of less than 0.004 wt.-%, while the catalyst produced accordingto Comparison Example 1 has a sulphur content of 0.155 wt.-%.

Activity Test 1:

The catalyst produced according to Examples 1 and 2 as well as accordingto Comparison Example 1 was subjected to a conversion of propane asactivity test under the test conditions below.

Test Conditions:

Particle size: 0.5-1.25 mm Temperature profile: room temperature (RT) →550° C. (5 h) → RT Heating rate: 10° C./min Cooling rate: 20° C./min COconcentration: 800 ppm Propane concentration: 200 ppm Gas hourly spacevelocity (GHSV): 100 000 h⁻¹ Initial weight: 7 g Catalyst volume: 14 ml

FIG. 2 shows the curve shapes of the measured propane conversions in theheating phase against the temperature, FIG. 3 the curve shapes of thepropane conversions during the constant temperature phase against timeand FIG. 4 shows the curve shapes of the propane conversions in thecooling phase against the temperature, wherein the curve shapes of thecatalysts of Examples 1 and 2 and Comparison Example 1 are denoted bysquares, circles and triangles respectively.

In the heating phase, the two catalysts according to Example 1 andComparison Example 1 display the same activity and achieve a conversionof approximately 95% (FIG. 2). During the constant temperature phase,the activity of the catalyst calcined in air according to ComparisonExample 1 clearly reduces, whereas the catalyst calcined under argonaccording to Example 1 displays almost the same activity over the wholeconstant temperature phase (FIG. 3). In the cooling phase, the catalystaccording to Example 1 also displays an increased activity compared withthat of Comparison Example 1 (FIG. 4). The curve shapes for the catalystaccording to Example 1 are almost identical in the heating and coolingphases (FIGS. 2 and 4).

The thermally aged catalyst according to Example 2 displays a clearlyreduced activity in the range of lower temperatures, but achieves theconversion of the unaged catalyst according to Example 1 at atemperature of 550° C. (FIG. 2).

COMPARISON EXAMPLE 2

20 g of powdery aluminium silicate zeolite material of the structuretype MFI (ZSM-5) in the ammonium form with an Si/Al atomic ratio of 27was impregnated with 3 wt.-% platinum (calculated as metal and relativeto the weight of the zeolite material and the platinum) in the form of(NH₃)₄Pt(NO₃)₂ by means of the incipient wetness method.

After the impregnation, the zeolite material was dried over night at atemperature of 120° C.

After the drying, the impregnated zeolite material was calcined in anargon atmosphere over a period of 5 h at a temperature of 790° C. Theheating rate from room temperature to 300° C. was 0.3° C./min, theheating rate from 300° C. to 790° C. was 4° C./min and the argonvolumetric flow rate during the heating and calcining phase was 2 l/min.The decomposition of the (NH₃)₄Pt(NO₃)₂ proceeds in a reductive manner,with the result that Pt of oxidation state 0 forms during the calcining.

COMPARISON EXAMPLE 3

A catalyst was produced analogously to Comparison Example 2, with theonly difference that a powdery aluminium silicate zeolite material ofthe structure type Beta (BEA) in the H form with an Si/Al2 atomic ratioof 35 was used as zeolite material.

EXAMPLE 3

A catalyst was produced analogously to Comparison Example 2, with thedifferences that a powdery aluminium silicate zeolite material of thestructure type Beta (BEA) in the H form with an Si/Al2 atomic ratio of35 was used as zeolite material, that the heating rate from roomtemperature to 790° C. was 2° C./min and that after the calcining thezeolite material loaded with platinum was reduced at a temperature of300° C. by means of a gas containing 5 vol.-% hydrogen in nitrogen (2l/min) over a period of 5 h. The heating rate was 2° C./min.

XRD Measurement 2:

The catalysts produced according to Example 3 and according toComparison Examples 2 and 3 were measured by X-ray diffractometry. Themeasured XRD spectra are represented in FIG. 5 in sections, wherein thespectrum of Example 3 and of Comparison Examples 2 and 3 are given thereference numbers 11, 13 and 12 respectively.

The XRD spectrum of the catalyst produced according to Example 3displays no Pt reflections at a 2-theta value of about 40°, whereas theXRD spectra of the catalysts produced according to Comparison Examples 2and 3 display clear Pt reflections. In fact, the signal at a 2-thetavalue of about 40° is the Pt(110) reflection.

The absence of Pt reflections in the catalyst according to Example 3 isan indication that no larger platinum particles have formed on the outersurface of the zeolite material and the platinum is present in thezeolite material predominantly in highly dispersed form.

Activity Test 2:

The catalysts produced according to Example 3 as well as according toComparison Examples 2 and 3 were subjected to a conversion of propane asactivity test under the test conditions below.

Test Conditions:

Particle size: 0.5-1.25 mm Temperature profile: room temperature (RT) →550° C. Heating rate: 10° C./min CO concentration: 800 ppm Propaneconcentration: 200 ppm Gas hourly space velocity (GHSV): 100 000 h⁻¹Initial weight: 7 g Catalyst volume: 14 ml

FIG. 6 shows the curve shapes of the measured propane conversions in theheating phase against the temperature, wherein the curve shape of thecatalyst according to Example 3 as well as those according to ComparisonExamples 2 and 3 are given the reference numbers 11, 13 and 12respectively. The activity test clearly shows the increased activity ofthe catalyst according to the invention produced by means of the methodaccording to the invention.

The light-off temperatures at which 50% of the propane used is convertedare 243° C. for the catalyst produced according to Example 3 and 498° C.and 356° C. for the catalysts produced according to Comparison Examples2 and 3 respectively.

1-17. (canceled)
 18. A catalyst comprising an open-pored supportmaterial and platinum of oxidation state 0, characterized in that an XRDspectrum of the catalyst is free of signals of elemental platinum. 19.The catalyst according to claim 18, characterized in that the catalystcomprises 1 to 5 wt. % platinum.
 20. The catalyst according to claim 18,characterized in that the support material is a zeolite material of thestructure type Beta. 21-22. (canceled)